Polyvinyl chloride resin compositions comprising a polyvinyl chloride resin together with a plasticizer have widely been used as a material for medical instruments such as, for example, medical tubes such as catheters, and medical bags such as blood bags, liquid medicine bags and drainage bags, because flexibility of the composition may be adjusted over a wide range by varying an amount of the plasticizer, and the composition has good moldability, adhesion, processability, heat resistance and kink resistance and is less costly. However, when a molded article composed of a polyvinyl chloride resin composition comprising a plasticizer is brought into contact with body fluids such as blood or with various aqueous solutions, the plasticizer or other additives may elute.
In general, a resin composition for medical instruments is desired not to cause elution of additives such as a plasticizer. Further, the resin composition for medical instruments is desired to be heat stable, because the medical instruments are necessarily sterilized.
Various methods have been proposed foe reducing the elution. For example, it is known to add a specific silicone oil to a polyvinyl chloride resin composition comprising di(2-ethylhexyl)phthalate (DOP) as a plasticizer (see the following Patent Literature 1). It is also proposed to add epoxidized vegetable oil hewing a peroxide number of 10 or less to a polyvinyl chloride resin composition comprising the DOP as a plasticizer (see the following Patent Literature 2). However, in reality, epoxidized vegetable oils having peroxide numbers of 5 or more only are described and reduction of the elution is not enough.
Also, it is proposed to substitute bis(2-ethylhexyl)terephthalate (DOTP) for the conventional DOP as a plasticizer to be added to a polyvinyl chloride resin (see the following Patent Literatures 3 to 5). These Patent Literatures do not refer to application of the polyvinyl chloride resin compositions to medical instruments or on reduction of elution. Further, these polyvinyl chloride resin compositions are inferior in heat stability and processability.